| 1. |
|
|
| 2. |
- Eriksson, Elin, 1989-, et al.
(författare)
-
Electron Acceleration in a Magnetotail Reconnection Outflow Region Using Magnetospheric MultiScale Data
- 2020
-
Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 47:1
-
Tidskriftsartikel (refereegranskat)abstract
- We study Magnetospheric MultiScale observations in the outflow region of magnetotail reconnection. We estimate the power density converted via the three fundamental electron acceleration mechanisms: Fermi, betatron, and parallel electric fields. The dominant mechanism, both on average and the peak values, is Fermi acceleration with a peak power density of about +200 pW/m3. The magnetic field curvature during the most intense Fermi acceleration is comparable to the electron gyroradius, consistent with efficient electron scattering. The peak power densities due to the betatron acceleration are a factor of 3 lower than that for the Fermi acceleration, the average betatron acceleration is close to zero and slightly negative. The contribution from parallel electric fields is significantly smaller than those from the Fermi and betatron acceleration. However, the observational uncertainties in the parallel electric field measurement prevent further conclusions. There is a strong variation in the power density on a characteristic ion time scale.
|
|
| 3. |
- Eriksson, Elin, 1989-, et al.
(författare)
-
Electron Energization at a Reconnecting Magnetosheath Current Sheet
- 2018
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:16, s. 8081-8090
-
Tidskriftsartikel (refereegranskat)abstract
- We present observations of electron energization within a sub-ion-scale magnetosheath current sheet (CS). A number of signatures indicate ongoing reconnection, including the thickness of the CS (similar to 0.7 ion inertial length), nonzero normal magnetic field, Hall magnetic fields with electrons carrying the Hall currents, and electron heating. We observe localized electron acceleration and heating parallel to the magnetic field at the edges of the CS. Electrostatic waves observed in these regions have low phase velocity and small wave potentials and thus cannot provide the observed acceleration and heating. Instead, we find that the electrons are accelerated by a parallel potential within the separatrix regions. Similar acceleration has been reported based on magnetopause and magnetotail observations. Thus, despite the different plasma conditions in magnetosheath, magnetopause, and magnetotail, the acceleration mechanism and corresponding heating of electrons is similar. Plain Language Summary Magnetic reconnection is an important physical energy conversion process in astrophysical and laboratory plasmas. The easiest place to analyze magnetic reconnection is in near-Earth space. Due to lack of sufficient electron resolution of previous spacecraft missions, there are many unanswered questions regarding electron heating and acceleration processes at small scales. In particular, the regime where thermal pressure dominates over magnetic pressure, the most common state of plasmas in the Universe, is little explored. In this letter we study such a regime using the four-spacecraft Magnetospheric Multiscale mission. We analyze a reconnecting current sheet in the magnetosheath. We show that electrons are energized by a parallel potential, similar to what has been observed in the different plasma regimes the magnetopause and magnetotail. Thus, despite different plasma conditions, a similar acceleration mechanism and corresponding heating of electrons is occurring in all these regions.
|
|
| 4. |
- Eriksson, Elin, 1989-
(författare)
-
Electron energization in near-Earth space : Studies of kinetic scales using multi-spacecraft data
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plasma, a gas of charged particles exhibiting collective behavior, is everywhere in the Universe. The heating of plasma to millions of degrees and acceleration of charged particles to very high energies has been observed in many astrophysical environments. How and where the heating and acceleration occur is in many cases unclear. In most astrophysical environments, plasma consists of negative electrons and positive ions. In this thesis we focus on understanding the heating and acceleration of electrons. Several plasma processes have been proposed to explain the observed acceleration. However, the exact heating and acceleration mechanisms involved and their importance are still unclear. This thesis contributes toward a better understanding of this topic by using observations from two multi-spacecraft missions, Cluster and the Magnetospheric MultiScale (MMS), in near-Earth space.In Article I we look at magnetic nulls, regions of vanishing magnetic field B believed to be important in particle acceleration, in the Earth's nightside magnetosphere. We find that nulls are common at the nightside magnetosphere and that the characterization of the B geometry around a null can be affected by localized B fluctuations. We develop and present a method for determining the effect of the B fluctuation on the null's characterization.In Article II we look at a thin (a few km) current sheet (CS) in the turbulent magnetosheath. Observations suggest local electron heating and beam formation parallel to B inside the CS. The electron observations fits well with the theory of electron acceleration across a shock due to a potential difference. However, in our case the electron beams are formed locally inside the magnetosheath that is contrary to current belief that the beam formation only occurs at the shock.In Article III we present observations of electron energization inside a very thin (thinner than Article II) reconnecting CS located in the turbulent magnetosheath. Currently, very little is know about electron acceleration mechanisms at these small scales. MMS observe local electron heating and acceleration parallel to B when crossing the CS. We show that the energized electrons correspond to acceleration due to a quasi-static potential difference rather than electrostatic waves. This energization is similar to what has been observed inside ion diffusion regions at the magnetopause and magnetotail. Thus, despite the different plasma conditions a similar energization occurs in all these plasma regions.In Article IV we study electron acceleration by Fermi acceleration, betatron acceleration, and acceleration due to parallel electric fields inside tailward plasma jets formed due to reconnection, the so called tailward outflow region. We show that most observations are consistent with local electron heating and acceleration from a simplified two dimensional picture of Fermi acceleration and betatron acceleration in an outflow region. We find that Fermi acceleration is the dominant electron acceleration mechanism.
|
|
| 5. |
|
|
| 6. |
- Löfström Engdahl, Elin, 1983, et al.
(författare)
-
Purification of used scintillation liquids containing the alpha emitters americium and plutonium
- 2015
-
Ingår i: Journal of Radioanalytical and Nuclear Chemistry. - : Springer Science and Business Media LLC. - 0236-5731 .- 1588-2780. ; 303:2, s. 1133-1136
-
Tidskriftsartikel (refereegranskat)abstract
- In Sweden, alpha radioactive waste liquids withan activity over some kBq per waste container cannot besent for final storage. Therefore, in this work, a method fora purification of alpha active scintillation cocktails wasdeveloped. Until today (March, 2013) more than 20 L ofscintillation liquids have successfully been purified fromamericium and plutonium. The products of the process area solid fraction that can be sent to final storage and apractically non-radioactive liquid fraction that can be sentto municipal incineration.
|
|
| 7. |
- Norgren, Cecilia, et al.
(författare)
-
Electron Reconnection in the Magnetopause Current Layer
- 2018
-
Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 123:11, s. 9222-9238
-
Tidskriftsartikel (refereegranskat)abstract
- The electron dynamics within thin current sheets plays a key role both for the process of magnetic reconnection and other energy transfer mechanisms but, from an observational point of view, is not well understood. In this paper we report observations of a reconnecting current sheet with intermediate guide field B-G = 0.5B(in), where B-in is the magnetic field amplitude in the inflow regions. The current sheet width is comparable to electron spatial scales. It shows a bifurcated structure and is embedded within the magnetopause current layer with thickness of several ion scales. The electron scale current sheet has strong out-of-plane and in-plane currents, Hall electric and magnetic fields, a finite magnetic field component normal to the current sheet, and nongyrotropic electron distributions formed due to finite gyroradius effects at the boundary of the current sheet. Comparison between test particle simulations and electron data shows that electrons approaching from the edge of the largest magnetic curvature are scattered to perpendicular pitch angles in the center of the current sheet while electrons entering from the opposite side remain close to field aligned. The comparison also shows that an observed depletion in phase space at antiparallel pitch angles can be explained if an out-of-plane electric field, which due to the guide field is close to antiparallel to the magnetic field, is present in the center of the current sheet. This electric field would be consistent with the reconnection electric field, and we therefore interpret the depletion of electron phase space density as a manifestation of ongoing reconnection.
|
|
| 8. |
- Oka, M., et al.
(författare)
-
Electron Power-Law Spectra in Solar and Space Plasmas
- 2018
-
Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 214:5
-
Forskningsöversikt (refereegranskat)abstract
- Particles are accelerated to very high, non-thermal energies in solar and space plasma environments. While energy spectra of accelerated electrons often exhibit a power law, it remains unclear how electrons are accelerated to high energies and what processes determine the power-law index delta . Here, we review previous observations of the power-law index delta in a variety of different plasma environments with a particular focus on sub-relativistic electrons. It appears that in regions more closely related to magnetic reconnection (such as the 'above-the-looptop' solar hard X-ray source and the plasma sheet in Earth's magnetotail), the spectra are typically soft (delta greater than or similar to 4). This is in contrast to the typically hard spectra (delta less than or similar to 4) that are observed in coincidence with shocks. The difference implies that shocks are more efficient in producing a larger non-thermal fraction of electron energies when compared to magnetic reconnection. A caveat is that during active times in Earth's magnetotail, delta values seem spatially uniform in the plasma sheet, while power-law distributions still exist even in quiet times. The role of magnetotail reconnection in the electron power-law formation could therefore be confounded with these background conditions. Because different regions have been studied with different instrumentations and methodologies, we point out a need for more systematic and coordinated studies of power-law distributions for a better understanding of possible scaling laws in particle acceleration as well as their universality.
|
|
| 9. |
- Philipsson, Anna, 1978-, et al.
(författare)
-
”Just in TIME” - Intervention med dans och yoga för flickor med funktionell magsmärta och IBS
- 2019
-
Konferensbidrag (refereegranskat)abstract
- Bakgrund och syfteFunktionell magsmärta drabbar många barn i skolåldern, mestadels flickor. Det kan leda till minskad livskvalitet, skolfrånvaro, sämre sömn, försämrade kamratkontakter och ökad vårdkonsumtion. Det vetenskapliga underlaget för interventioner vid långvarig smärta hos barn är begränsat. Dans kan öka rörelseglädje och förbättra kroppskännedom, vilket i sin tur påverkar självtillit och kan öka psykiskt välbefinnande. Yoga kan ge mental avslappning och reducera stressreaktioner. Syftet med studien är att utvärdera effekten av en intervention med dans och yoga på återkommande magsmärta, stress och depressiva symtom samt på funktion i vardagen hos flickor 9-13 år som har funktionell buksmärta och IBS.MetodEn randomiserad kontrollerad studie genomförs med forskningspersoner som identifieras via diagnosregister samt barnmottagningarna i Västerås och Örebro, samt från primärvården. Interventionen består av dans och yoga med fokus på rörelseglädje, gemenskap och kravlöshet, och utförs som gruppaktivitet två ggr/veckan under 8 månader. Primärt utfall är förändring av magsmärta efter 8 mån. Flickorna följs upp under fem år avseende magsmärta, självskattad hälsa, stress och psykiskt välmående, fysisk aktivitet och skolfunktioner. Vidare studeras kostnad i relation till nytta.Resultat/(Planerade studier)Projektet pågår och de första resultaten beräknas publiceras hösten 2019. Projektet utvärderas både kvalitativt, genom intervjuer med flickor och vårdnadshavare, och kvantitativt, genom bland annat analys av smärtdagböcker, upplevd hälsa, stress samt med en hälsoekonomisk analys. Därutöver utvärderas salivkortisol och faeces som objektiva mått. KonklusionStudien förväntas leda till ökad kunskap om icke-farmakologiska insatser för barn samt hur behandlingsinsatser för målgruppen kan breddas med ett kostnadseffektivt alternativ till ”standard care”.
|
|
| 10. |
- Svensson, Elin, 1980, et al.
(författare)
-
Design of heat exchanger networks with good controllability
- 2018
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- One important way to improve the energy efficiency of chemical process plants is to improve the heat integration within and between industrial processes. This is accomplished by recovering excess process heat at high temperatures and using it to replace primary heating at lower temperatures through a heat exchanger network. However, as a process becomes more heat integrated, process control may become more difficult. Poor control performance can, in turn, easily lead to increased costs that outweigh the predicted energy cost savings. It is therefore essential to model and analyze the effect of the process changes and address the identified potential control challenges. However, the majority of existing methods for controllability assessment of heat exchanger networks only consider steady-state properties, and not the dynamic aspects, which in reality can seriously affect process control characteristics. With better methods for controllability analysis alternative design options could be evaluated and compared more reliably at an earlier design stage. This report proposes the basic structure of a step-wise approach for integrating dynamic considerations into the design process for heat recovery improvements in process industry, and suggests suitable methods and tools to be used for the different steps of the proposed framework. As part of this, recent work that has been performed to evaluate and improve the methods used in controllability assessment is outlined. Additionally, a number of areas are identified in which significant further efforts are required before a complete controllability assessment framework can be specified and a toolbox for integrated design and controllability analysis can be developed. One central area requiring continued research and development is to define an adequate controllability index for use in heat exchanger network design. For example, it is relatively easy to argue that some of the commonly applied controllability measures are insufficient since they are based on steady-state system interactions only. However, as illustrated in the report, alternative measures of system interactions that take dynamics into account suffer from other drawbacks, of which one is scaling dependency. Nevertheless, these are interesting for further development of a new controllability assessment method, since the issues with scaling can possibly be dealt with using an approach evaluated in this project. Another area where further work is needed is to develop tools with some level of built-in support for formulation of dynamic models of heat exchanger networks. Model simplifications, or other means of handling the large model sizes typically resulting from dynamic modelling of heat exchanger networks may also be needed in order to overcome difficulties in model simulation and analysis. In addition to the development needs related to individual assessment steps, there is an apparent need for appropriate protocols for information transfer and conversion of models between different tools. This report gives an overview of insights revealed in recent research with respect to the controllability of heat exchanger networks. Through this research, the knowledge for continuing the effort to define a better controllability index for heat exchanger networks has been improved.
|
|
